I recently had my 2010 197 put in the water and discovered I had water coming into the bilge.
I then had my dealer/local Mastercraft repair shop take the boat out of the water.
They say it was a leaking seal around the bilge plug. The plug was apparently sealed with silicone. "the repair tech said, "this happens all the time {to new boats}."

Really.

One buddy of mine said, " I wouldn't seal anything below the waterline with silicone.
Plus, you have a new 60k + boat' it shouldn't do that!"

This is my feeling. Brand new boat shouldn't be leaking. Plus the MC shop tells me this is not under warranty. So the repair guy sealed it with 5200 caulk. Tough stuff. But why is this not used in the manufacturing in the first place? Again, this is a 60k+ boat! Doesn't seem right that MC would use an inferior product when using a 5200 caulk wouldn't have cost them much more. Now I have to pay for my dealer to haul the boat out/in and do this work all due to a poor choice in caulk? If I had not noticed this in the very beginning my boat might have sank!

My question is:
Is this in fact standard manufacturing process for MC (or any other manufacturer) to seal with silicone at the under-the-waterline water points-of-entry (bilge plug, raw water intake, rudder post, stuffing box, bolts through the transom at the swim step)? IT seems to me that if this is a manufacturing choice that causes me to spend money on the boat in the first 3 years then I should not have to pay for the repair of an issue that could have/should have been done right in the first place. Car manufacturers have recalls for these issues, right?

I pulled my rudder box on my 06 x9 tonight. It was sealed with Silicone as well. I am actually very happy they didnt use 5200 on it as it makes it significantly harder to remove. I would suggest 4200 as it is removable on a part - such as a rudder box with could require removal for repair or rebuilding after time.

I was surprised it was silicone on mine as most threads i have read mentioned it being a difficult remove based on sealant. I would say out of the factory is should be a marine sealant, not a pliable silicone. 5200 and 4200 are both marine sealants from 3M, 4200 just doesnt require heat and debond solution to remove.

How can I test to identify the source?
Also, what's the procedure to reseal the plug?

Hopefully it's out of the water -
any chance the threads are damaged / cross-threaded and not sealing?

Testing could be tricky - I would try - (dreaming this up as we go) - a plunger that fits in this zone.

A low profile test plug /teflon tape on threads/ so plunger can slid over it when bilge filled with water an inch or so.
Compress plunger & release a few times to fill plunger as much as possible with water - then apply constant pressure - filled plunger of water over plug.
By yourself - may have to set up video to see drain plug up close - review to see trace of leak.

If not leaking around flange of drain - thats a good sign threads are maybe the cause.

If plunger is a no go - may have to fill it more to create enough pressure to see leak.
Couple drops of dish soap makes water wetter testing.
Good luck - image would help.

That is the transducer for you depth gauge. It reads depth right through the hull. Typically mounted in a puddle of epoxy - it looks like it just popped off the smooth surface. I would take some course grit sand paper (80 grit or so) and rough up the area where it was mounted. Then clean that area really good with alcohol...mix up some two-part epoxy and re-attach. Done.